Wireless sensor networks are being increasingly used to realize applications in domains like healthcare monitoring, building automation and lighting, or wireless connectivity and controls. This, in parallel with the explosive growth of wireless applications and services, has led to a scarcity of available licensed spectrum for allocation. To deal with the need to improve utilization of radio spectrum, more flexible spectrum sharing models like secondary spectrum sharing are being considered. As a consequence, an increasing portion of next-generation wireless networks will likely operate on secondary basis on licensed spectrum. Such operation refers to the situation where a secondary system is allowed to operate on the same radio spectrum that has been allocated to a licensed system (also referred to as a primary system). The secondary system is constrained to operate under the condition that its transmission does not result in harmful interference to the primary system beyond a certain specified limit. This requirement can be met by spectrum sensing, which involves the determination that a channel is vacant before it can be used by the secondary system.
Devices included in Personal area networks, or in body sensor networks, that operate on secondary basis on licensed spectrum require operating protocols carrying out sensing features.
Body sensor networks comprise many sensor nodes, used for measuring physiological parameters and for transmitting them to a sensor hub or gateway. The topology of such networks is generally asymmetric, since sensor nodes are required to be energy-efficient, while the sensor hub, or gateway, can be more complex with greater hardware and software capabilities. Moreover, in these networks, the data flow is largely from the sensor nodes to the hub or gateway.
Several sensing protocols have been proposed, wherein, if a communication link is to be established between a pair of transmitter-receiver on a secondary basis, the transmitter first performs sensing to determine whether or not a licensed system signal is active on the channel. If the channel is found vacant, the transmitter can begin communication with the receiver. These protocols, wherein the receiver has no role in sensing, may be termed transmitter-centric. It has been noticed that, if such protocols are highly efficient in some wireless networks, they appear as being problematic when it comes to body sensor networks.
Indeed, in body sensor networks, sensor nodes, which are required to transmit information to a sensor hub, or gateway, must have a long life-time as compared to their resource capacity, since these nodes are generally intended to be placed on a human body, and thus can not carry out large batteries, and can not be wirely powered either. Accordingly, having each sensor node perform periodic sensing, as required in a transmitter-centric network, is highly energy-consuming for sensor nodes, and require frequent replacement or load of these nodes, which is almost incompatible with correct operation of body sensor networks.
Moreover, in the context of solutions for achieving secondary spectrum access in the 2.36-2.4 GHz band which is being proposed for medical body area networks, it can be noted that radios based on the IEEE 802.15.4 Physical/MAC layer may be reused with suitable protocol modifications. In the current standard specification, a sporadic channel assessment is adopted instead of continuously sensing the medium. Once an empty channel is found, the network is setup on that channel. Different radios contend for that channel through carrier sense multiple access protocols or variations of it. Such a mechanism is suitable for coexistence in unlicensed spectrum. However it is problematic if used for secondary spectrum access, due to regulatory constraints on interference avoidance to licensed systems. It is an object of the invention to use the proposed protocol as a MAC modification such that in combination with the 802.15.4 PHY, the radios may be used to meet regulatory constraints of secondary spectrum use.